enthalpy

[ en-thal-pee, en-thal- ]

noun

, Thermodynamics.

, plural en·thal·pies.

1. a quantity associated with a thermodynamic system, expressed as the internal energy of a system plus the product of the pressure and volume of the system, having the property that during an isobaric process, the change in the quantity is equal to the heat transferred during the process. : H

enthalpy

/ ˈɛnθəlpɪ; ɛnˈθæl- /

noun

1. a thermodynamic property of a system equal to the sum of its internal energy and the product of its pressure and volume H Also calledheat contenttotal heat

enthalpy

/ ĕn′thăl′pē /

1. A partial measure of the internal energy of a system. Enthalpy cannot be directly measured, but changes in it can be. If an outside pressure on a system is held constant, a change in enthalpy entails a change in the system's internal energy, plus a change in the system's volume (meaning the system exchanges energy with the outside world). For example, in endothermic chemical reactions, the change in enthalpy is the amount of energy absorbed by the reaction; in exothermic reactions, it is the amount given off.
2. See also thermodynamics

Word History and Origins

Origin of enthalpy¹

1925–30; < Greek enthálp ( ein ) to warm in ( en- en- ² + thálpein to warm) + -y ³

Word History and Origins

Origin of enthalpy¹

C20: from Greek enthalpein to warm in, from en- ² + thalpein to warm